It was Veterans Day, far from the parades, and Michael Schoenbaum was standing on the stage of the library in Dorchester that honors a war hero and president named Jack Kennedy, explaining something that all Americans need to hear.

Schoenbaum works at the National Institute of Mental Health and has compiled the definitive study on why soldiers are killing themselves at alarming rates. Last year, more American soldiers died by their own hand than by the enemy’s.

Almost every day, he said, combat veterans from the wars in Iraq and Afghanistan are killing themselves. Between 2004 and 2008, the suicide rate among active service soldiers doubled.

Sitting in the audience, Tom “TJ” Brennan could only nod in rueful recognition. His service dog, Luke, sat at his feet.

“I worry about this,” he said. “I worry about my Marines.”

TJ Brennan grew up in Randolph and joined the Marines when he was 17. By the time the wars in Iraq and Afghanistan were raging, he was ready to lead. He was a squad leader, but experience can’t avoid rocket-propelled grenades and the one that landed next to him in Afghanistan knocked him out.

He realized he had a traumatic brain injury and post-traumatic stress long after his visible wounds healed. He told his Marines first, and they hugged him because they’re Marines. He told his commanders next and they said all the right things to his face and talked about him behind his back.

“I wasn’t as upset about what they said about me compared to what message that sent to the junior Marines, who were just preparing for combat,” TJ Brennan said. “The command was basically telling them, if you need help, you’re weak.”

Last December, two years after a general pinned a Purple Heart on him in Afghanistan, TJ Brennan retired after nearly 10 years a Marine, and he entered a dark place.

“I felt completely worthless,” he said. “My identity was being a Marine. Now it was gone.”

He wanted to be gone. He swallowed a bottle of sleeping pills. Then he lay down and waited to die. As he waited, he imagined his daughter living with the shame of a father who killed himself. And then TJ Brennan ran to the bathroom and the same fingers he had used to kill the enemy he used to save himself. His trigger finger went down his throat and he threw up.

His journey through the mental health care system, as porous for our vets as it is for everybody else, was worse than combat.

“We can do better for our vets,” he said. “We’ve got to do better for our vets.”

The day before TJ Brennan was sitting at the Veterans Day forum at the Kennedy Library organized by Home Base, the program established by the Red Sox and Massachusetts General Hospital to treat the invisible wounds of war, he was standing with me on I Street in South Boston. The Quencher, an old neighborhood pub in Southie, is closing and held a block party. I knew it would be the biggest gathering of Marines since Fallujah. Besides, it was the Marine Corps’ birthday.

I figured TJ would get a kick out of meeting all the old Marines, including the Quencher owners, Dodo Nee and Nino Sances. Dodo and Nino told him he was with his brothers now.

“Semper Fi,” Dodo said, shaking TJ’s hand.

“Semper Fi,” TJ said back to him.

TJ Brennan smiled and took it all in, but I noticed he was preoccupied. He regarded the crowd and wondered if he should have brought Luke. But it was more than that. He kept looking around, as if he had lost something. And then he told me.

“I lost one of my Marines two days ago,” TJ Brennan said. “He had a wife. He had a little girl, 4 months old. But he had his demons and they wouldn’t leave him alone. He killed himself.”